Project 2-4: Getting a 2-Stroke Motor in a 4-Stroke Frame, Part 5

May. 10, 2011 By Rick "Superhunky" Sieman
Hereís the stock RM 250 pipe jammed into place. As you can see, there's a whole lot hanging out.

In part four of our project bike, we got the gearbox and the carburetor problem figured out. Now comes the hard part of our project: figuring out where and how the pipe is to be mounted.

Project 2-4 Stories:

Part 4

Part 3

Part 2

Part 1

Ideally, we wanted a typical high pipe, but the two-stroke barrel is much bigger and wider than the four-stroke motor that was in there, so we had to go with the low pipe after much fiddling around.

Another view of the pipe showing that it just doesn't fit.

One good thing we noticed about the possible pipe installation was that there was a good amount of room under the motor and between the frame rails. Therefore, if we had to run a low pipe, it would be tucked in very nicely and very little of the pipe would be hanging down.

Write all the major measurements of the pipe down on paper before you start cutting. This way, you have a reference point as you do your surgery.

A very important thing: before you start to cut on the pipe in any way whatsoever, measure all of the areas of the pipe that will receive cuts. This means the head pipe, the first cone, the belly or center section of pipe, the second cone and the stinger. This way, if you have any questions, you can refer back to your absolutely correct original dimensions.

The head pipe is placed into the RM 250 barrel at this point.

We tried the pipe in various high positions that you can see from the photos but rather quickly abandoned this idea, as way too much of the pipe stuck out and would be nothing but a leg burner.

The remainder of the exhaust pipe.

The best thing you can do with starting to fabricate a pipe, is to position the head pipe as best you can. We cut it off and this gave us a very good starting point.
Now follow along and see what we accomplished.

The tab on the frame rails must be removed for proper pipe clearance.

Both sides have a tab that must be removed.

With both of the tabs removed, you can see that there is plenty of room for the pipe within the frame rails.

The first cut on the stock pipe is removing the head pipe from the belly of the pipe.

You can see that this section fits neatly within the frame rails.

A couple of ordinary bungee cords will hold the piece of pipe in the proper position.

The head pipe lines up with the first section, but there's a pretty huge gap in there that must be filled in later.

A piece of metal is welded into the pipe sections to hold up in the proper position. At this point, is not necessary to finalize any welding on the joints.

You can see how the pipe now lines up with the two sections joined.

The rest of the sections can now be lightly welded in place. It will be necessary to make cuts almost all the way through the pipe and then bend the pipe to the desired shape.

At this point, we now have the basic shape of the pipe intact, but it's necessary to bend the final section up so the stinger clears properly.

Here's the basic pipe in place, and as you can see, very little hangs down low.

Again, a bungee cord is used to hold the stinger up in place while the mounts for the pipe are fabricated.

The front mounting bracket was made of two pieces of metal rather than one, because it's stronger that way. This mounting bracket carries a lot of weight of the pipe.

A center mount was made and bolts through the bottom of the engine in an existing hole.

Now the pipe can be properly welded and the big gaps are filled in.

Very little of the pipe hangs down low, and what does is close to the rear tire.

After all the welding, the pipe gets a coat or two of high-temperature engine enamel.

Check out other stories in the Project 2-4 Build:

Part 4

Part 3

Part 2

Part 1

A small aluminum muffler gets slipped into place.

A hanging bracket was fabricated from an aluminum strap.

Here's the finished pipe. Itís tucked in nicely and everything is out of the way.

This side view shows that there is not a whole lot of stuff waiting to be crunched by hazards on the trail. All things considered, we rate this pipe as a success. Newsletter
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